FIG. 27 depicts an example of an Internet Protocol (IP) network. In such a network, it is important to identify the communication route on the network because of the following reasons, for example. Specifically, first, as depicted in FIG. 28, this is because it is necessary to identify a route at which the failure occurs, when loss of packets occurs. Second, this is because it is necessary to confirm whether or not the communication route is a route assumed at the network design. Third, this is because it is necessary to confirm whether or not packets are bypathed so as not to affect the service, when the maintenance work or the like is carried out.
By the way, Open Shortest Path First (OSPF) protocol is frequently used for the routing control in the IP network. In OSPF, the respective network apparatuses (e.g. routers) exchange packets called Link State Advertisement (LSA), and generates and holds a topology and routing table.
Conventionally, a route monitoring server to capture packets flowing in a network is provided for the network in which the routing by OSPF is carried out, in order to identify the communication route in the network by collecting LSA. For example, in FIG. 27, the route monitoring server captures packets flowing in a router E, and generates and holds the same topology and same routing table as that in the router.
On the other hand, in OSPF, when there are plural communication routes (called Equal Cost Multi-Path (ECMP)) having the same cost to a certain destination, the load can be distributed to the respective communication routes. Incidentally, the allocation to the respective communication routes is carried out for each combination of the source address and destination address, for example.
For example, in the network depicted in FIG. 27, when, as the ECMP from the router G to the route H, there are a first route “router G-router A-router E-router N1-router D-router H” and a second router “router G-router B-router C-router D-router H”, packets sent from “12.0.0.0/8” to “10.0.0.0/8” are transmitted through the first and second routes, distributively. Here, the route monitoring server can identify the first and second routes from the routing table.
However, because the allocation to the respective communication routes is carried out for each combination of the source address and destination address, the route monitoring server cannot identify, from the routing table, which route the packets pass through.
Specifically, it is impossible for conventional arts to identify the communication route of the packets in a server that monitors the network when there are plural communication routes through which the packets are presumed to pass in the network.